1. Field of the Invention
The present invention relates to image projection engines. More particularly, the present invention relates to an image projection engine that provides a polarized image for use in, for instance, a xe2x80x9cfoldedxe2x80x9d projection system.
2. Description of the Related Art
High power lamps are used for illumination applications beyond typical incandescent and fluorescent lamps. One type of lamp known as a high intensity discharge (HID) lamp consists of a glass envelope which contains electrodes and a fill which vaporizes and becomes a plasma when the lamp is operated.
Recently, a patent issued for a high power lamp that utilizes a lamp fill containing sulfur or selenium or compounds of these substances. U.S. Pat. No. 5,404,076, issued to Dolan et al. and entitled xe2x80x9cLamp Including Sulfurxe2x80x9d discloses an electrodeless lamp utilizing a fill at a pressure at least as high as one atmosphere. The fill is excited at a power density in excess of 50 watts per square centimeter. A lamp utilizing the fill is excited at a power density of at least 60 watts per square centimeter. The Dolan et al. patent is incorporated herein by reference Other pressures and power densities can be employed.
Projecting systems are used to display images on large surfaces, such as movie or television screens and computer displays. For example, in a front projection system, an image beam is projected from an image source onto the front side of a reflection-type angle transforming screen, which then reflects the light toward a viewer positioned in front of the screen. In a rear projection system, the image beam is projected onto the rear side of a transmission-type angle transforming screen and transmitted toward a viewer located in front of the screen.
Projection engine designs are not new. For example, in U.S. Pat. No. 5,453,859 (hereby incorporated by reference), a system is shown that uses a polarization beam splitter along with a dichroic xe2x80x9cX-cubexe2x80x9d to create a color image. Referring to FIG. 14 of that patent, it is seen that polarized light from a light source 91 is reflected by a polarization beam splitter to a dichroic prism 95. The reflected light is S-polarized, or polarized normal to the plane of incidence within the prism 93. This S-polarized light is then passed through a quarter wave plate 94, which circularly polarizes that S-polarized light. For each pixel that is in the xe2x80x9coffxe2x80x9d position, that circularly polarized light is reflected unchanged by the corresponding pixel of a reflective LCD 96, 97, and 98. Then, that circularly polarized light is restored to its original S-polarized state on the return path through the quarter wave plate 94. That light is then reflected back towards the light source by the prism 93.
For pixels that are to be lit, the LCDs 96, 97, and 98 convert some of the circularly polarized light to elliptically polarized light. When this light is passed through the quarter wave plate 94, the light passed will not be solely S-polarized, but will instead include a P-polarized component, which is passed through the prism 93, through a projection lens 99, and into whatever projection system is used.
Displaytech, Inc., in a 6-page technical disclosure entitled xe2x80x9cFLC/VLSI Display Technologyxe2x80x9d and dated Dec. 1, 1995; Parfenov et al., in xe2x80x9cAdvanced optical schemes with liquid crystal image converters for display applications,xe2x80x9d SPIE Proceedings, Volume 2650, pages 173-179 (Jan. 29-31, 1996); and Baur et al., in xe2x80x9cHigh performance liquid crystal device suitable for projection display,xe2x80x9d SPIE Proceedings, Volume 2650, pages 226-228 (Jan. 29-31, 1996), disclose background information on the use of liquid crystal devices to process video images. These papers are hereby incorporated by reference.
The present invention provides an improved projection engine. Polarized light from a light source is reflected by a polarizer/analyzer (such as a 3M DBEF material) which reflects only the S-polarized components of light and transmits P-polarized components of light.
One of the polarized components of light is passed to an image engine that forms an image by shifting the polarity of portions of the light. For example, the S-polarized light can be passed to a dichroic X-cube beam splitter/combiner (or other beam splitter/combiner for splitting the S-polarized light into red, green, and blue components when light passes through the beam splitter/combiner in a first direction and for combining red, green, and blue components when light passes through the beam splitter/combiner in a second direction) which provides red, green, and blue light to spatial light modulator type liquid crystal displays. Alternatively, the beam splitter/combiner could be omitted and a color sequential technique could instead be used to provide colored light. In addition, a combination of the two techniques can be employed. The liquid crystal displays alter the polarity of the S-polarized light so that the reflected light is S-polarized, P-polarized, or elliptically polarized with both S-polarized and P-polarized components, depending on the amount of light that is to be transmitted to the display and the type of spatial light modulator. This light, if the polarity is unchanged, is reflected back to the light source by the polarizer/analyzer. Any P-polarized components, however, are passed through the polarizer/analyzer and on to the display.
Using this system, a variable intensity of each color can be applied with each pixel, and each resulting pixel is generated through the coaligned colors of light. Further, the optics are highly efficient, because virtually all of the source light of an xe2x80x9conxe2x80x9d pixel is transmitted for display and virtually all of the source light of an xe2x80x9coffxe2x80x9d pixel is returned to the lamp where its energy may be recovered.
The beam splitter/combiner is chosen such that there is either no alteration of the polarity of light passing therethrough (the preferred situation) or a consistent, predictable alteration of the polarity so that compensation for the alteration of polarity can be made by controlling the LCDs. For example, if a beam splitter/combiner that is chosen for use alters the polarity of green light passing back and forth through it one quarter wave total, the LCDs for the green light would be adjusted such that if one wanted a dark pixel, one would cause the LCD to alter the polarity back one quarter wave in the opposite direction to end up with a green light beam that is reflected back at the source from the DBEF reflective surface.
The present invention preferably comprises a projection display apparatus comprising:
a source of rays of polarized light;
a 3M DBEF reflecting polarizer aligned at an angle to the rays of polarized light for passing substantially all of the rays of polarized light which are polarized in a first direction and for reflecting substantially all of the rays of polarized light which are polarized in a second direction;
a beam splitter/combiner, having a first, primary incidence plane aligned with the reflected polarized light for splitting the rays of polarized light which are polarized in the second direction into blue, green, and red light rays;
a first reflecting polarizing LCD for receiving the blue light rays from the beam splitter/combiner, shifting the polarization of none, some, or all of the blue light rays, and directing the blue light rays back into the beam splitter/combiner;
a second reflecting polarizing LCD for receiving the green light rays from the beam splitter/combiner, shifting the polarization of none, some, or all of the green light rays, and directing the green light rays back into the beam splitter/combiner;
a third reflecting polarizing LCD for receiving the red light rays from the beam splitter/combiner, shifing the polarization of none, some, or all of the red light rays, and directing the red light rays back into the beam splitter/combiner; and
a lens for receiving and transmitting substantially all of the rays of polarized light which are polarized in the first direction and which have passed from the beam splitter/combiner through the DBEF reflecting polarizer.
Preferably, the source of rays of polarized light comprises a xe2x80x9clight-pumpedxe2x80x9d source that can re-absorb and re-emit unused reflected light; when a xe2x80x9clight-pumpedxe2x80x9d source is used, the apparatus can also include a mirror aligned at substantially a 90xc2x0 angle to the rays of polarized light as the rays exit the source for reflecting back to the source the rays of polarized light which are polarized in a first direction and which pass through the DBEF reflecting polarizer without first passing through the beam splitter/combiner. The source of rays of polarized light preferably includes a reflecting polarizing filter for passing substantially all of the rays of polarized light which are polarized in the second direction and for reflecting substantially all of the other rays of light. The source of rays of polarized light preferably also comprises a reflecting filter for passing substantially all rays of blue light, green light, and red light, and for reflecting substantially all rays of light which are not blue light, green light, or red light.
A condenser lens can advantageously be interposed along the path of the rays of polarized light between the source of rays of polarized light and the DBEF polarizing reflector.
The source of rays of polarized light can advantageously comprise:
an electrodeless lamp body that defines a chamber;
a gas contained within the chamber;
electrodes positioned externally of the lamp chamber for producing radio frequency energy that excites the gas, forming a plasma light source of intense heat that emits a light beam, wherein the electrodes are not subjected to the intense heat generated at the plasma; and
a reflector positioned next to the lamp body for redirecting some of the light emitted by the light source back to the lamp using the reflector so that the lamp reabsorbs light energy to intensify the light source, wherein the reflector includes a polarizing filter that is positioned to receive and polarize the light beam.
The projection display apparatus of the present invention can advantageously be used as an image source in a projection apparatus for producing an image display on a display surface comprising a display surface, an optical device which is reflective of some light and transmissive of other light; and means for transmitting light from the image source to the display surface such that the light travels an image path which reaches the optical device twice on its way to the display surface.
The present invention also comprises a method of producing a visual image comprising:
providing a source of rays of polarized light;
directing the rays of polarized light onto a 3M DBEF reflecting polarizer aligned at an angle to the rays of polarized light for passing substantially all of the rays of polarized light which are polarized in a first direction and for reflecting substantially all of the rays of polarized light which are polarized in a second direction;
reflecting the light rays which are aligned in the second direction from the 3M DBEF reflecting polarizer into a beam splitter/combiner having a first, primary incidence plane aligned at an angle to the 3M DBEF reflecting polarizer for splitting the rays of polarized light which are polarized in the second direction into blue, green, and red light rays;
valving the blue light rays in a first reflecting polarizing LCD for receiving the blue light rays from the beam splitter/combiner, by shifting the polarization of none, some, or all of the blue light rays 90xc2x0, and directing the blue light rays back into the beam splitter/combiner;
valving the green light rays in a second reflecting polarizing LCD for receiving the green light rays from the beam splitter/combiner, by shifting the polarization of none, some, or all of the green light rays 90xc2x0, and directing the green light rays back into the beam splitter/combiner;
valving the red light rays in a third reflecting polarizing LCD for receiving the red light rays from the beam splitter/combiner, by shifting the polarization of none, some, or all of the red light rays 90xc2x0, and directing the red light rays back into the beam splitter/combiner;
electrically controlling the LCDs;
reflecting the blue, green, and red light rays polarized in the second direction from the 3M DBEF reflecting polarizer back to the source of rays of polarized light; and
transmitting the blue, green, and red light rays polarized in the first direction through the 3M DBEF reflecting polarizer to a lens which transmits the blue, green, and red light rays polarized in the first direction to produce a visual image. In this method, the source of rays of polarized light preferably comprises a xe2x80x9clight-pumpedxe2x80x9d source that can re-absorb and re-emit unused reflected light. The method preferably further comprises the step of reflecting back to the source of rays of polarized light the rays of polarized light which are polarized in a first direction and which pass through the DBEF reflecting polarizer without first passing through the beam splitter/combiner from a mirror aligned at substantially a 90xc2x0 angle to the rays of polarized light as the rays exit the source.
The source of rays of polarized light preferably includes a source of light and a reflecting polarizing filter for passing substantially all of the rays of polarized light which are polarized in the second direction and for reflecting substantially all of the other rays of light.
The source of rays of polarized light can also include reflecting filter for passing substantially all rays of blue light, green light, and red light, and for reflecting substantially all rays of light which are not blue light, green light, or red light.
In the method of the present invention, the LCDs are preferably analog LCDs.
The apparatus of the present invention can be broadly described as a projection display apparatus comprising:
an optically pumpable source of rays of polarized light that can re-emit unused light returned to it;
a wide angle reflecting polarizer for passing substantially all of the rays of polarized light which are polarized in a first direction and for reflecting substantially all of the rays of polarized light which are polarized in a second direction;
at least one reflecting polarizing LCD for receiving the light rays from the reflecting polarizer, shifting the polarization of none, some, or all of the light rays, and directing the light rays back towards the wide angle reflecting polarizer;
a lens for receiving and transmitting substantially all of the rays of polarized light whose polarization has been shifted by the at least one reflecting polarizing LCD; and
means for returning the rays of polarized light whose polarization has not been shifted by the at least one reflecting polarizing LCD to the source of rays of polarized light to optically pump the source.
The method of the present invention can broadly be described as a method of producing a visual image comprising:
providing an optically pumpable source of rays of polarized light that can re-emit unused light returned to it;
directing the rays of polarized light onto a wide angle reflecting polarizer for passing substantially all of the rays of polarized light which are polarized in a first direction and for reflecting substantially all of the rays of polarized light which are polarized in a second direction;
using at least one reflecting polarizing LCD, shifting the polarization of none, some, or all of the light rays, and directing the light rays back towards the wide angle reflecting polarizer;
receiving with a lens and transmitting through the lens substantially all of the rays of polarized light whose polarization has been shifted by the at least one reflecting polarizing LCD; and
returning the rays of polarized light whose polarization has not been shifted by the at least one reflecting polarizing LCD to the source of rays of polarized light to optically pump the source.